In recent years, increasing numbers of resin components have come into use to provide lightweight vehicles in the automobile industry. Active research has been performed aiming to develop resin-based shock absorbing interior and exterior members (crushable parts) for automobiles. In load-displacement curves obtained from a high speed compression test assuming automobile collisions, shock absorbing members are required to (1) show a large displacement when the load becomes zero due to destruction and (2) suffer from little change in load attributable to a displacement under a large load (gives a high-load square wave). Many of the approaches attempted at present are focused on specially shaped members such as honeycomb structures, foams, hollow structures, and ribbed molded articles. On the other hand, few efforts are being made in the field of material development, and there are expectations for novel materials.
Major shock absorbing materials include thermoplastic elastomers such as polyurethane. Being low in strength, rigidity, and heat resistance, however, thermoplastic elastomers tend to be useful only for limited uses, and in recent years, many material development efforts are focused on polymer alloys.
Some thermoplastic resin compositions suitable for shock absorbing members have been disclosed, including highly shock absorbing thermoplastic resin compositions produced by blending a thermoplastic resin and a rubbery polymer with a reactive functional group and while controlling the phase structure formation (for example, see Japanese Unexamined Patent Publication Nos. 2006-89701 and 2008-156604). Others disclose polyamide resin compositions high in strength, rigidity, impact resistance, and heat resistance that contain a polyamide resin, inorganic filler, and thermoplastic resin having a reactive functional group, with the inorganic filler and the thermoplastic resin having a reactive functional group independently dispersed in the polyamide resin (for example, see Japanese Unexamined Patent Publication Nos. 2007-238752 and 2009-144058). Also disclosed are fiber reinforced resin compositions consisting mainly of highly shock absorbing resin composition (A) produced by blending resin (A1) with resin (A2) having a reactive functional group while controlling the phase structure formation, as well as resin (B) and fibrous filler (C) (for example, see International Publication WO 2010/107022). In addition, we have disclosed polyamide resin compositions consisting mainly of a highly shock absorbing resin composition produced by blending a polyamide resin with a rubbery polymer having a reactive functional group while controlling the phase structure formation, combined with a dendritic polyester resin, acid anhydride, and glass fiber (for example, see Japanese Unexamined Patent Publication No. 2011-195814).
JP '701 and JP '604 disclosed resin compositions that increase in rupture elongation with an increasing tension speed, but in a high speed compression test for square prism shaped molded articles produced by molding these resin compositions, the load was low. In addition, it was difficult to obtain a square wave although the displacement when load becomes zero was large. Compared to this, the resin compositions described in JP '752 and JP '058 were produced without controlling the reaction between a polyamide resin and a thermoplastic resin with a reactive functional group, and in a high speed compression test for square prism shaped molded articles produced by molding these resin compositions, the displacement when the load becomes zero was small. In addition, it was difficult to obtain a square wave. Furthermore, the resin compositions described in WO '022 contained only a small amount of resin with a reactive functional group, though having a specific phase structure, and in a high speed compression test for square prism shaped molded articles produced by molding these resin compositions, the displacement when the load becomes zero was sometimes small and it was sometimes difficult to obtain a square wave. When these conventional, generally known resin compositions are used to produce shock absorbing members, particularly shock absorbing interior and exterior members for automobiles that receive large energy at the time of a collision, it has been necessary to process them into complicated shapes such as honeycomb structures, foams, hollow structures, and ribbed molded articles, as in the case of conventional materials.
It is thus a major problem to provide a thermoplastic resin composition suitable for shock absorbing members that are high in strength, rigidity, and heat resistance and are resistant to fracture and able to exhibit a high-load square wave in a high speed compression for square prism or other simple shaped molded articles.